3d Max model issues

[wmgeorge]

DesignSpark Mechanical, I mentioned it above. It's the free cut down version of SpaceClaim.

I use QCAD for 2D drawing its a lot like AutoCAD LT but only priced at $37 US for the download. For the rest I use Fusion 360, free for hobbyists and startups. Pretty darn good, a slight learning curve and that's going away as I learn. I used AutoCAD and AutoCAD LT for years before getting into 3D printing.

[ajmadison]

if your going to print something then you should design the model for printing. everything needs to be 100% watertight. no stray unconnected surfaces, holes or bad triangles in the mesh. any errors will cause slicers to go a bit wacky and not know what to do.

Of course I find this posting after I figured this out last night. I had some initial success, chopping a detail part off from a much bigger mesh created by, I *believe*, lightwave, and it printed as I expected. I tried making some mods to the part. At which point S3D got confused because of all the detached meshes and surfaces, and filled in all of the intentional hollows in the part. I rebuilt the part, using the original mesh as a guide to creating "solid" tubes and boxes. And one complex piece, willingly converted to a mesh, and I could fill all of the 'holes.' Now S3D doesn't fill the whole thing. Not sure I understand why I decided to insert "bridging" in the center of the piece. But I still have some of the original mesh, which I will try replacing and see if this makes the bridging go away.

[ednisley]

Not sure I understand why ...

All mesh repair programs face the same task: converting a non-manifold collection of triangles into something that can represents a valid solid geometry to be sliced and printed. Because the algorithms don't have any other information about your intended shape, they make the least-intrusive repairs that remove the defects. Those repairs may produce geometric changes that are not at all what you expect, however.

Because each mesh repair program applies a different set of rules in a different order, they all produce different results. That leads some folks to claim that the Most Excellent Repair Program A produces much better results than either Half-Hearted B or Obviously Junk C. That's certainly true, when all the models have a common defect that the rules in A handle better than either B or C.

Part of the problem comes from using a mesh modeling program (intended to produce lush images) as a 3D mechanical design tool: mesh modelers have no concept of "solid" geometry, so it's trivially easy to produce a mesh that looks good when rendered, but doesn't describe an actual solid object in 3D. Sketchup earned a considerable degree of notoriety for its crappy models, but all mesh modelers suffer the same limitation; some have plugins that attempt to repair their meshes, with varying results.

The unpleasant fact remains that a non-manifold model can and will produce weird results that change unpredictably as you tinker with the not-quite-3D mesh. The fault lies in the model, not in the mesh repair program or the slicer.

Bottom line: if you're using a mesh modeler, run the STL file through different repair programs until the repaired mesh has no (visible) artifacts, then preview the actual G-Code produced by the slicer to ensure that the nozzle paths produce the same 3D shape you want. If the slicer complains that the mesh isn't manifold, that means you must do a better repair job; there's no shortcut!

[Tim]

I'm trying to print a 20 story high rise building at 1/16 scale. I realize I'll probably need to split it in two and glue it together at that scale.

Just wanted to point out that 20 stories at 1/16 scale means that your model will be 20 divided by 16 = 1.25 actual stories tall, or about 15 feet high, which is going to require more than two printed pieces. To get it down to two pieces, you'd be doing more like 1/150 scale. . .